There are a number of security documents used regularly in everyday life which require authentication at one point or another. For example, security documents such as identity cards used in industry, as well as passports are regularly required to be checked to ensure that they are genuine and not a clever forgery aimed at deceiving the person to whom the security document is produced as verification of identity. Similarly, exchangeable documents such as bills of lading, cheques, bonds, share certificates and other negotiable instruments as well as hard currency such as banknotes are regularly required to be proven to be authentic when they are exchanged. Accordingly, a number of techniques have been developed to ensure the authenticity of security documents of this type.
It is known to incorporate sophisticated design features into a number of security documents such as currency and banknotes with the aim of making them difficult to copy. Alternatively it has been known to incorporate watermarks or other design features such as metallic threads that can be identified by human inspection of the security document. Unfortunately a number of these “first wave” authentication techniques have become redundant as technological advances have meant that forgers have been able to reproduce security documents including these features rendering them redundant as a means of providing security document authenticity.
In order to stay ahead of forgers a number of other design features have been developed that rely on the use of complementary technology to determine the presence of the design feature in the security document to be authenticated. Examples of such features include the presence of a magnetic strip containing information that can be read by a scanner (an example of this is a barcode). Technology of this type requires the use of a reading means that can verify the authenticity of the strip in the security document. Other techniques include the use of fluorescent dyes that only fluoresce when exposed to light of a specific wavelength (typically ultraviolet (UV)) which once again requires the presence of a UV lamp in order to authenticate the security document. It has also been known to incorporate certain rare earth elements that have multiple-photon mechanisms that can be activated by lasers at specific wavelengths into the security document. Whilst these have been successful in overcoming forgeries to a greater or lesser extent they all still require the presence of a complementary device of some sort to determine the authenticity of the security document. Whilst this is acceptable in certain high security arrangements where unit cost is not a critical issue and the point of authentication of the security document can be accurately defined (such as with a passport at the customs check at an airport), these techniques are not amenable in all circumstances. In particular they are unsuitable in circumstances where there are an unusually high number of transactions or in circumstances where the geographical location of the transaction is not well defined. An example of such a transaction is a transaction involving the handing over of money.
Accordingly there is still the need to develop alternative techniques for the authentication of security documents especially techniques that do not require the use of a complementary device in the authentication process.
In the past the use of piezoelectric films has been proposed for use in relatively stiff security documents. For instance, U.S. Pat. No. 5,566,982 and JP 2004 78731 disclose laminated piezoelectric films suitable for application to an identity card or credit card. However, such films are relatively rigid and inflexible and, being crystalline, become hard and brittle when stretched, and have been found not to be appropriate in the case of more flexible documents comprising flexible sheets, such as banknotes, which are often folded and crumpled in use. It is therefore desirable to develop better materials and methods that enable piezoelectric polymeric material to be applied to documents of such a flexible nature.
Throughout this specification reference may be made to published documents for the purpose of describing various aspects of the invention. However, no admission is made that any reference cited in this specification constitutes prior art. In particular, it will be understood that the reference to any published document herein does not constitute an admission that any of these documents forms part of the common general knowledge in the art in any country.
Throughout the description and claims of this specification, the word “comprise” and variations of the word, such as “comprising” and “comprises”, is not intended to exclude other additives, components, integers or steps.